September 03, 2008

Romans and AIDS resistance

Scientists believe the invading Romans caused the loss of a genetic shield that makes some people resistant to infection by the Aids virus, HIV.

The gene variant, called CCR5-Delta32, impairs the ability of HIV to enter white blood cells.

People with the mutation are not as easily infected by the virus and take longer to develop full-blown Aids.

Generally, only Europeans and western Asians carry the variant, which becomes less widespread as you move south.

More than 15% of people in some parts of northern Europe have CCR5-Delta32, compared with fewer than 4% of Greeks.

...

He does not think the Romans spread a different version of the gene into their colonies by breeding with the natives.

A more likely explanation, he believes, is that they introduced a fatal disease to which carriers of the CCE5-Delta32 variant were unusually susceptible.

New Scientist magazine reported: "As the Romans moved north, this disease killed people with the variant.

It's hard to envision a disease that would be limited to the territory of the Roman Empire. The Roman frontier was fluid, with both Romans trading beyond it, and barbarians moving into Roman territory; it's hard to imagine how a disease could be "contained" within the territory of the Empire. Moreover, I don't really see a good candidate for a really dramatic Empire-wide epidemic, which would surely have been noticed by historians.

In countries inside the borders of the empire for longer periods, such as Spain, Italy and Greece, the frequency of the CCR5-delta32 gene, which offers some protection against HIV, is between 0% and 6%.

Countries at the fringe of the empire, such as Germany, and modern England, the rate is between 8% and 11.8%, while in countries never conquered by Rome, the rate is greater than this.

...

However, some researchers believe that infections may have played a role - but in reverse -increasing rather than decreasing the frequency of the variant.

Researchers at the University of Liverpool suggested that the variant may have offered protection against pandemics such as the Black Death which swept Europe on a regular basis during and after the Roman era.

These, said the Liverpool researchers, were illnesses which may have been lethal to people without the gene variant, raising its frequency from one in 20,000 people to approximately 10% in Northern Europe.

Infection, Genetics and Evolution doi:10.1016/j.meegid.2008.08.007

Is the European spatial distribution of the HIV-1-resistant CCR5-Delta32 allele formed by a breakdown of the pathocenosis due to the historical Roman expansion?

Eric Faure and Manuela Royer-Carenzi

We studied the possible effects of the expansion of ancient Mediterranean civilizations during the five centuries before and after Christ on the European distribution of the mutant allele for the chemokine receptor gene CCR5 which has a 32-bp deletion (CCR5-Delta32). There is a strong evidence for the unitary origin of the CCR5-Delta32 mutation, this it is found principally in Europe and Western Asia, with generally a north-south downhill cline frequency. Homozygous carriers of this mutation show a resistance to HIV-1 infection and a slower progression towards AIDS. However, HIV has clearly emerged too recently to have been the selective force on CCR5. Our analyses showed strong negative correlations in Europe between the allele frequency and two historical parameters, i.e. the first colonization dates by the great ancient Mediterranean civilizations, and the distances from the Northern frontiers of the Roman Empire in its greatest expansion. Moreover, other studies have shown that the deletion frequencies in both German Bronze Age and Swedish Neolithic populations were similar to those found in the corresponding modern populations, and this deletion has been found in ancient DNA of around 7000 years ago, suggesting that in the past, the deletion frequency could have been relatively high in European populations. In addition, in West Nile virus pathogenesis, CCR5 plays an antimicrobial role showing that host genetic factors are highly pathogen-specific. Our results added to all these previous data suggest that the actual European allele frequency distribution might not be due to genes spreading, but to a negative selection resulting in the spread of pathogens principally during Roman expansion. Indeed, as gene flows from colonizers to European native populations were extremely low, the mutational changes might be associated with vulnerability to imported infections. To date, the nature of the parasites remains unknown; however, zoonoses could be incriminated.

Fact: Generally, only Europeans and western Asians carry the variant... More than 15% of people in some parts of northern Europe have CCR5-Delta32, compared with fewer than 4% of Greeks.

Speculation: the invading Romans caused the loss of a genetic shield that makes some people resistant to infection by the Aids virus, HIV

Specially as we know this is not the only S/N differential within Europe.

Isn't much more logical that a founder effect caused the pre-existent gene to be multiplied by 3 in Northern Europe accidentally? There does not seem to be any evolutionary cause, any adaptative historical pressure acting. Nor does appear any visible "Roman" genetic component anywhere. Nor seems Greece any particularly good reference for Southern Europe overall...

Is the European spatial distribution of the HIV-1-resistant CCR5-Delta32 allele formed by a breakdown of the pathocenosis due to the historical Roman expansion?

Romans had "Malaria" in their homeland, in south latium until 1930, but there aren't rchaeological or historical evidence that they brought the mosquito (Zanzara Anopheles) in the rest of Europe. If it is true that there is a correlation among the decrement of CCR5-Delta32 in the places where Roman or Italic colonies were founded it can be for genetics mixture onlt, but I am a lot of sceptic that this has happened.

The Roman Empire was not spread by Romans, that is a fallacy. The number of Romans was very small relative to the number of paid mercenaries who could become Roman citizens after 25 years service. Granted most of the leaders were Roman citizens, but the guys doing the fighting and intermingling with the locals were from all over western asia and africa. So, it would be surprising to me that "Romans" spread HIV? Possibly "African" mercenaries would be a better guess???

This is true since the II century AD, before the legionaries were only italics, the first non italic legion was the IV Alaude, a legion enlisted by Caesar for the war in Gaul, in the Cisalpin Gaul. But we don't have to think only about the legionaries, a city lives of commerces and a colony doesn't have only legionaries, it was inhabited from civil people too, but you are right, the colonizers were too few numerous to cause a similar effect.

I think it's just another lazy deduction with very poor grounds. From the BBC version of this news item:

Countries at the fringe of the empire, such as Germany, and modern England, the rate is between 8% and 11.8%, while in countries never conquered by Rome, the rate is greater than this.

England was as much part of the Roman Empire as Greece and, in fact, more likely to have been affected by military presence and resettlement, yet its parameter is closer to "barbarian" Germany than to "Roman" Greece.

In general legions were sent to the borders, specially the northern border with the Germans and Picts and the eastern border with Persia/Parthia, where the threat was greater. I don't make much sense of Roman military having more impact in Greece than in England. The opposite may well be true instead.

As mentioned, there would be other demic flows, specially Mediterranean (and Atlantic) trade but this is probably not much different from older connections along the same maritime axis.

In any case, we do have an idea of how Europeans tend to cluster genetically and we know that there is no Roman nor Rome-related clustering of any sort. It is just another element of the regional diversity (in which the N/S axis seems quite relevant).

Anyhow, following with the Roman hypothesis, the BBC article says:

However, the researchers do not believe that the genetic difference is due to Roman soldiers or officials breeding within the local population - history suggests this was not particularly widespread, and that invading and occupying armies could have been drawn not just from Italy but from other parts of the empire.

Instead, they say that the Romans may have introduced a disease to which people with the CCR5-Delta32 variant were particularly susceptible. This tallies with some other theories of why some have the gene variant, and some do not.

Researchers at the University of Liverpool had suggested that the variant could have offered protection against pandemics such as the Black Death which swept Europe on a regular basis during and after the Roman era.

This is contradictory: if the alelle offered protection against the plague, then it should be more important in the Mediterranean (and not the other way around). But I guess that the authors may have meant the opposite: that it added susceptibility to the plague. In any case, the Medieval Black Death should have balanced things, as it affected all Europe massively (only Poland and the Northern Basque Country/Beárn were spared).

The article follows: These, said the Liverpool researchers, were viral illnesses...

The plague is not viral but bacterian (Y. pestis). What again suggests that either the journalist or the researchers are kind of confused.

In any case the tentive Roman explanation makes little sense on light of the overall European genetic structure. A neutral non-adaptative explanation seems very likely to explain the relatively minor regional differences in this alelle.

You could use similar criteria to show that Roman armies created the distribution of eye color in Europe. (After all blue eyes reaches it's highest frequency in those areas where Rome never conquered. Yeah, a Roman virus must be responsible.)

Crimson Guard-Do you mean that Romans gave HIV/AIDS to the world?I thought AIDS came from eating African Monkey Meat-Did Romans eat African Monkey Meat?If they did I guess they get what they deserve.Personally I wouldn't want AIDS no matter what my ethnicity-I mean since when was it BETTER to be Scandinavian with AIDS?I wouldn't want it AIDS at all.I hope not to get AIDS since I'm not a drug addict or a homosexual.If you don't have it ,then it doesn't matter what your ethnic resistance is,now does it? How many Mediterraneans have AIDS compared to Northern Europeans?I would think the Mediterranean genes are more civilized-if you CAN get AIDS,then I think you would be more careful NOT to get it.

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